The Basics of Interpretation

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Pulmonary Function Testing

Jennifer Hale, M.D.Valley Baptist Family Practice Residency

Objectives

Identify the components of PFTs

Describe the indications

Develop a stepwise approach to interpretation

Recognize common patterns

Apply this information to patient care

Pulmonary Function TestingJennifer Hale, M.D.

Which of the following is used to follow disease severity inCOPD patients?

a. Total lung capacity (TLC)b. Degree of responsiveness to bronchodilatorsc. Forced vital capacity (FVC)d. Forced expiratory volume in 1 seconde. Diffusing capacity (DLCO)

A 36yo WF, non-smoker, presents to your office for follow-upof ‘recurrent bronchitis.’ You suspect asthma and decideto order spirometry. Which of the following would youinclude in your prescription for testing?

a. Diffusing Capacity (DLCO)b. If no obstruction present, add trial of bronchodilatorc. If no obstruction present, perform methacholine challenged. Flow volume loope. b and c

A 68yo HM is admitted to the ICU with acute respiratorydistress. A CXR obtained in the ED demonstratesbilateral pulmonary infiltrates, and his DLCO iselevated. What is the most likely diagnosis?

a. Pulmonary edemab. Aspiration pneumonitisc. Pulmonary embolid. Alveolar hemorrhagee. Interstitial lung disease

The Purpose

Provide quantifiable, reproduciblemeasurement of lung function

Description

Spirometry Flow Volume Loop Bronchodilator response Lung volumes Diffusion capacity (DLCO) Bronchoprovocation testing Maximum respiratory pressures Simple and complex cardiopulmonary exercise

testing

Indications — Diagnosis

Evaluation of signs and symptoms- SOB, exertional dyspnea, chronic cough

Screening at-risk populations

Monitoring pulmonary drug toxicity

Abnormal study- CXR, EKG, ABG, hemoglobin

Preoperative assessment

Smokers > 45yo(former & current)

Evaluation of occupational symptoms

Indications — Prognostic

■ Assess severity

■ Follow response to therapy

■ Determine further treatment goals

■ Referral for surgery

■ Disability

Spirometry

Simple, office-based

Measures flow, volumes

Volume vs. Time

Can determine:- Forced expiratory volume in one second (FEV1)- Forced vital capacity (FVC)- FEV1/FVC- Forced expiratory flow 25%-75% (FEF25-75)

Lung Volumes

Spirometry

Normal Spirometry

Obstructive Pattern

■ Decreased FEV1

■ Decreased FVC

■ Decreased FEV1/FVC- <70% predicted

■ FEV1 used to follow severity in COPD

Obstructive Lung Disease —Differential Diagnosis

Asthma

COPD - chronic bronchitis

- emphysema

Bronchiectasis

Bronchiolitis

Upper airway obstruction

Restrictive Pattern

Decreased FEV1

Decreased FVC

FEV1/FVC normal or increased

Restrictive Lung Disease—Differential Diagnosis

Pleural

Parenchymal

Chest wall

Neuromuscular

Spirometry Patterns

Bronchodilator Response

Degree to which FEV1 improves with inhaledbronchodilator

Documents reversible airflow obstruction

Significant response if:- FEV1 increases by 12% and >200ml

Request if obstructive pattern on spirometry

Flow Volume Loop

“Spirogram”

Measures forced inspiratory and expiratoryflow rate

Augments spirometry results

Indications: evaluation of upper airwayobstruction (stridor, unexplained dyspnea)

Flow Volume Loop

Upper Airway Obstruction

Variable intrathoracic obstruction

Variable extrathoracic obstruction

Fixed obstruction

Upper Airway Obstruction

Lung Volumes

Measurement:- helium- nitrogen washout- body plethsmography

Indications: - Diagnose restrictive component

- Differentiate chronic bronchitis from emphysema

Lung Volumes – Patterns

Obstructive - TLC > 120% predicted

- RV > 120% predicted

Restrictive- TLC < 80% predicted- RV < 80% predicted

Diffusing Capacity

Diffusing capacity of lungs for CO

Measures ability of lungs to transport inhaled gasfrom alveoli to pulmonary capillaries

Depends on:- alveolar—capillary membrane- hemoglobin concentration- cardiac output

Diffusing Capacity

Decreased DLCO(<80% predicted)

Obstructive lung disease

Parenchymal disease

Pulmonary vasculardisease

Anemia

Increased DLCO (>120-140% predicted)

Asthma (or normal)

Pulmonary hemorrhage

Polycythemia

Left to right shunt

DLCO — Indications

Differentiate asthma from emphysema

Evaluation and severity of restrictive lungdisease

Early stages of pulmonary hypertension

Expensive!

Case 1

CC/HPI: A 36yo WM, nonsmoker, presents to yourclinic with c/o episodic cough for 6mo. Alsoreports occasional wheezing and dyspnea withexertion during softball practice.

Exam: Heart RRR, no murmurs; Lungs CTAB, nolabored breathing

Based on your exam and a thorough review ofsystems, you suspect asthma and decide toorder spirometry for further evaluation.

Continued…

PFTs: FEV1 86% predicted FEV1/FVC 82% predicted

Flow Volume Loop: normal inspiratory andexpiratory pattern

You still suspect asthma. What is your nextstep in the workup of this patient?

Bronchoprovocation

Useful for diagnosis of asthma in thesetting of normal pulmonary function tests

Common agents:- Methacholine, Histamine, others

Diagnostic if: ≥20% decrease in FEV1

Continued…

↓SYMPTOMS

OBSTRUCTION?

YES NO

TREATBRONCHOPROVOCATION

Obstruction?TREAT

No Obstruction? Other Diagnosis

↓ ↓

PFT Interpretation Strategy

What is the clinical question?

What is “normal”?

Did the test meet American Thoracic Society(ATS) criteria?

Don’t forget (or ignore) the flow volume loop!

Obstructive Pattern — Evaluation

Spirometry FEV1, FVC: decreased FEV1/FVC: decreased (<70% predicted)

FV Loop “scooped”

Lung Volumes TLC, RV: increased

Bronchodilator responsiveness

Restrictive Pattern – Evaluation Spirometry

FVC, FEV1: decreased FEV1/FVC: normal or increased

FV Loop “witch’s hat”

DLCO decreased

Lung Volumes TLC, RV: decreased

Muscle pressures may be important

PFT Patterns

Emphysema

FEV1/FVC <70%

“Scooped” FV curve

TLC increased

Increased compliance

DLCO decreased

Chronic Bronchitis

FEV1/FVC <70%

“Scooped” FV curve

TLC normal

Normal compliance

DLCO usually normal

PFT Patterns

Asthma

FEV1/FVC normal or decreased

DLCO normal or increased

But PFTs may be normal bronchoprovocation

Questions?

References

1. Aboussouan LS, Stoller JK: Flow volume loops. UpToDate, 2006.2. Bahhady IJ, Unterborn J: Pulmonary function tests: an update. Consultant.

2003.3. Barreiro, TJ, Perillo I: An approach to interpreting spirometry. Am Fam

Physician. 2004 Mar 1;69(5):1107-14.4. Chesnutt MS, Prendergast TJ. Current Medical Diagnosis and Treatment.

New York: Appleton and Lange, 2006.5. Enright PL: Diffusing capacity for carbon monoxide. UpToDate, 2007.6. Enright PL: Overview of pulmonary function testing in adults. UpToDate,

2007.7. Irvin CG: Bronchoprovocation testing. UpToDate, 2006.8. West JB. Respiratory Physiology: The Essentials. Lippincot Williams &

Wilkins, 2000.